Device for driving a receiving teletypewriter, with correction of the drivepulse distortion



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ALDO CUPELLA United States Patent DEVICE FOR DRIVING A RECEIVING TELETYPE- WRITER, WITH CORRECTION OF THE DRIVE- PULSE DISTQRTION Aldo Cupella, Milan, Italy, assignor of one-half to Soc. Metallotecnica, Milan, Italy, a corporation of Italy Filed May 9, 1956, Ser. No. 583,846

Claims priority, application Italy June 10, 1955 7 Claims. (Cl. 178-69) As it is known, the correct operation of a teletypewriter essentially depends on the drive-pulse duration and amplitude. Such pulses in practice are deformed by the time constants of the connecting lines of the machines (in case of transmission by wire), or they may be deformed by the circuit constants of the radio receivers (in case of radio reception) and by the selective circuits (in case of transmission by carrier frequency). Such distortions are generally permanent in character, at least for the duration of a given transmission.

The present invention relates to a device for driving a receiving teletypewriter, with correction of the drive pulse distortion, whenever necessary, permitting the return of the pulses to the shape required for the correct operation of the machine.

The pulse correcting arrangement according to the invention comprises a pulse-repeating relay and a pair of thyratrons for driving the receiving relay of a teletypewriter. The pulse-repeating relay is a biased relay of the telegraphic type having a movable armature contact centered between two side contacts. The side contacts are coupled to the thyratrons to initiate conduction therein according to the operation of the armature contact. The repeating relay has a winding coupled to the input circuit, so that it responds to mark signals to operate the armature contact to one side contact and initiate conduction in one thyratron to thereby supply mark signals to the receiving relay of the teletypewriter, and it responds to space signals to operate the armature contact to the other side contact to initiate conduction in the other thyratron to deliver space signals to the receiving relay of the teletypewriter. Coupling is provided between the thyratrons to cut off either responsive to the initiation of conduction in the other. The thyratron circuit is arranged to deliver output signals having constant pulse amplitude and rise time to the teletypewriter receiving relay. The pulse receiving relay is provided with an adjustable arrangement for displacing the point of balance of the armature contact in relation to the side contacts to regulate the mark-to-space pulse ratio of the signal delivered by its contacts with respect to its winding current. Thus, it may be seen that an arrangement has been provided for supplying pulses having a corrected pulse ratio, and a constant pulse amplitude and rise time, for driving the receiving relay of the teletypewriter.

Further, according to the invention, the adjusting arrangement on the pulse repeating relay may comprise an auxiliary winding on the relay and means for adjusting the current through this auxiliary winding. To provide for the adjustment of the current, a potentiometer having a sliding tap is connected across the auxiliary winding, and a source of DC. power connected with one pole to the potentiometer tap and the other pole to a center tap of the auxiliary winding.

If additional current is needed for driving the teletypewriter, additional thyratrons may be connected in parallel with each thyratron of the pair.

2,981,795 Patented Apr. 25, 1961 In a specific arrangement according to the invention, the side contacts of the repeating relay are connected respectively to the grids of the thyratrons of the pair, .and the teletypewriter receiving relay is connected between the thyratron plates. A capacitor is so connected between the cathodes of the thyratrons that when conduction is initiated in either, a positive pulse is sent through this capacitor to cut off the other.

Further, according to the invention, an arrangement is provided for detecting and indicating the pulse ratio to aid in adjusting the regulating arrangement associated with the pulse repeating relay. The indication is preferably an optical representation of the pulse shape. In a specific embodiment, this arrangement comprises a disk driven by a synchronous motor with an oscillator and amplifier for supplying current to the motor at a frequency such that the disk is rotated in synchronism with the character repetition of the received telegraph signals. Two lamps are mounted on the disk circumferentially displaced by of the circumference and radially by an appreciable distance, and the lamps are lighted in accordance with the repeated mark and space pulses, respectively. The lamps may be connected across the cathode resistors, respectively, of the thyratrons of the pair.

Further, according to the invention, the input circuit for the pulse repeating relay includes two amplifier tubes, the first biased to cut oil and the other biased to be normally conducting. The principal winding of the repeating relay is connected between the plates of these two tubes. Alternating current telegraph signals of the type which are On for the mark signals and Oil for the space signals or vice versa, are converted to direct current signals by two separate rectifying circuits, the first supplying positive signals to the grid of the first tube, and the other supplying negative signals to the grid of the other tube. Thus, when the alternating current signals are in the On condition, the first tube is driven into conduction and the other is cut oif. The alternating current signals are obtained from an oscillator comprising a thyratron in a relaxation circuit which is normally biased to a blocking condition. This thyratron oscillator is started responsive to one type of pulses, such as the mark pulses, of the incoming signal. Amplifiers may be connected between the oscillator and the rectifier circuits.

The present invention is shown only by way of an example, in the accompanying drawings, wherein:

Fig. 1 is a generic diagram of the device;

Fig. 2 and Fig. 3 show some details of the same device.

According to Fig. 1, the pulse arriving in the form of a direct current (in case of direct transmission on wire), or as an alternating current (in case of radio reception from the receiver and the selecting circuits in case of transmission with carrying frequency on wire) releases the blocked oscillator l, the signal of which, amplified by the amplifying circuit 2, drives the electronic device 3 which in turn drives the very sensitive relay 4. Such relay, in its normal position, presents an armature contact that is equally spaced from the two side contacts and when driven by the pulse signals, closes either its right contact or its left contact according to the nature of the pulses, i.e. either mark or space pulses. By mechanically, or electrically, or magnetically displacing the balance center position of the armature contact 4 relatively to its two side contacts, the time necessary for the armature contact to go and close the right contact, will be made different from that necessary to go and close the left contact. The closing of side contacts due to the motion of the armature contact, causes the thyratrons 5 and 6 (or groups of thyratrons) to be alternatively started. Said thyratrons are so connected that the starting of the thyratron causes the thyratron 6 to be released, and vice versa, directly driving the relay 7 of the machine. In such a way the machine relay is double current driven thru pulses the amplitude of which may be maintained constant by means of a suitable stabilized feeding of the thyratrons, the wave front steepness of which depends only on the starting and releasing time of the thyratrons presented by that circuit, and the duration of which may be adjusted by mechanically, or electrically, or magnetically acting on the balance center position of the movable relay armature contact. To facilitate the adjustment of the pulse durationflthe pulse signals obtained from 5 and 6, or from one of them, are sent to an electronic device (for instance, a cathode-ray oscillograph), an electronic and mechanical device, or an electromechanical device, indicated on Fig. l by the number 8 and adapted to give an optical representation of the respective duration of the work and rest pulses.

According to Fig. 2, the driving pulse signal releases the oscillator with thyratron 1 that sends the pulse signal to the grids of the tubes 9 and 10, which amplify it and thru the rectifying groups 11 and 12, convert it at the same time, to two pulses, respectively a positive and a negative one, The positive pulse from the rectifying group 11 releases the tube 13 previously blocked by a fixed polarizing negative potential; the negative pulse from the rectifying group 12 blocks the tube 14 previously emitting its highest current. Thus, the winding 15 of the very sensitive relay 16 is passed in one direction by a part of the tube 14 current, in absence of a signal on the oscillator 1, and in the opposite direction by a part of the tube 13 current, when the oscillator 1 is released by the signal. Thus, when a signal arrives, the movable armature contact of the relay 16 passes from a side contact to the opposite one. The two winding sections 17 and 18 of an auxiliary winding of relay 16 conduct current in opposite directions having the same or different values according to the position of the slide of the potentiometer 19. It is therefore easily possible, by adjusting the potentiometer 19, to change the vibrating balance center position of the relay armature contact, it being thus possible to vary the mark pulse duration in respect to the space pulse duration. Thyratrons 20 and 21 are normally blocked by a negative biasing potential on their grids and may be released by closing the relay 16 armature contact on the side contacts, said contact closure causing the potential to change on the thyratron grids from a negative value to a positive one.

The starting of each of said two thyratrons determines the release of the other, because, in the starting moment for a tube, on the cathode of the other, thru a capacitor 22, a positive pulse is sent, having a considerable amplitude, sufficient to release it. The teletypewriter relay 23 placed between the plates of two thyratrons 20 and 21 is therefore partially passed in one given direction by the current of one of said thyratrons, in absence of a signal on the oscillator 1, and in the opposite direction, when the oscillator 1 is released by the signal. The amplitude equality of the two space and mark pulses and their constants in the time may be easily assured in this latter circuit by a suitable feeding stabilized potential for the thyratrons and by the constant value of the resistances, thru which the thyratron current must pass.

Fig. 3 is a diagrammatic representation of possible embodiment of an electronic-electromechanical device which gives a visualization of the pulse duration in order to make easy the adjustment. At 24 is indicated a variable oscillator generating a signal which, when amplified by the amplifier 25, is fed to the synchronous motor 26 that makes a number of revolutions per second equal to the number of characters written per second by the machine. Since the machine speed may be varied, the oscillator 24 also is Variable.

On the shaft of the motor 26 is fastened a disk which carries two fluorescent lamps 28 and 29 which have an angular distance from one another of ,6 of the circumference and which are placed, with respect to the center, at two radial dilferent lengths. Said lamps 28 and 29 are parallel-connected respectively to the cathode resistances of the thyratrons 20 and 21 of Fig. 2 and therefore alternatively they are lighted up according to the mark and space pulses.

Since eachcharacter received by the machine consists, according to the Baudot code, of the combination of five pulses to which other two pulses are added, ie one for beginning and one at the end of the transmission, that is seven pulses in total; when the disk 27 rotates at the same speed of the machine, as hereinafter defined, because the two lamps 28 and 29 are shifted one from another at an angular distance of of the circumference, two superposed luminous streaks are formed having circumferential lengths directly proportional to the duration of the respective mark and space pulses. On the basis of the image seen on the disk 27, it is possible easily to adjust the pulse duration by acting on the potentiometer 19 of Fig. 2. With the aim of better explaining the above matter, on Fig. 3 the images 30, 31, 32 of a typeare shown, as they result on the disk 27. The image 30 shows a correct reception, with mark pulses having the same or multiple duration of the space pulses; the image 31 shows a reception having for instance mark pulses having a duration much less than the space pulses and the image 32 shows an arrangement contrary to that of the image 31. In both cases of images 31 and 32 no reception on the machine is possible, Whilst a small adjustment of the relay 16 of Fig. 2, makes possible to have on the disk the image 30 that is to return to a correct reception for the teletypewriter. Being that the image is stopped on the disk 27 when the rotation speed of the same disk equals the teletypewriter writing, the above-mentioned device, by a suitable adjustment of the oscillator, 24, permits also the ready knowledge of the transmitting machine, the latter being possibly very important.

Though the present invention has been disclosed only by the above description, it is obvious that many changes and additions are possible, without departing from the spirit and scope of the same invention as defined by the following claims.

What is claimed is:

l. A pulse correcting arrangement for supplying signal current to the receiving relay of a teletypewriter in a sys tem wherein two-valued information signals are trans mitted, said arrangement comprising a source of alternating-current signals, a first electron tube having a control grid normally biased to cutoff, a first rectifying arrangement coupled between said source and said first tube for applying a positive potential to its grid to render it conductive responsive to output signals from said source, a second electron tube having a control grid and normally conducting, a second rectifying arrangement coupled be tween said source and said second tube for applying a negative potential to its grid to cut it off responsive to output signals from said source; a pulse repeating relay having a winding connected in the output circuits of said first and second tubes, and having contact means comprising a movable armature contact and two other contacts, one on each side of said armature contact; means responsive to one value of said information signals to block the supply of signals from said source to both of said rectifying arrangements to thereby cut oif direct-current output from the rectifying arrangements, and means responsive to the other value of said information signals to supply alternating current signals from said source to both of said rectifying arrangements to thereby produce direct-current output from the rectifying arrangements; means including said normal biasing of said electron tubes effective with no output from said rectifying arrangements to produce a first condition of current flow in said pulse repeating relay to operate said armature contact to one side contact, and means responsive to direct-current output from said rectifying arrangements to bias said electron tubes to produce a second condition of current flow in said pulse repeating relay to operate said armature contact to the other side contact; first and second thyratrons coupled respectively to said side. contacts, means for initiating conduction of said thyratrons alternately responsive respectively to closure of said side contacts, means for cutting off either thyratron responsive to the initiation of conduction in the other, means connecting said receiving relay in the output circuits of said thyratrons, means responsive to conduction in one of said thyratrons to produce a first output signal condition in said receiving relay and means responsive to conduction in the other thyratron for producing a second output signal condition in said receiving relay; circuit means including the thyratrons and the receiving relay to cause the output signals to said receiving relay to have constant pulse amplitude and rise time; manually adjustable means associated with said pulse repeating relay to displace the point of balance of said armature contact in relation :to said side contacts to regulate the pulse ratio of the output signals with respect to the current in said pulse-repeating-relay Winding; and means for detecting and indicating said pulse ratio to aid in adjusting said adjustable means.

2. A pulse correcting arrangement according to claim 1 wherein said source of alternating current signals comprises a relaxation oscillator including a thyratron having a control grid; a direct-current bias source connected to the last'said control grid to normally block the oscillator; wherein said means responsive to the other value of the. information signals to supply alternating current signals comprises means for applying a potential to the last said control grid to enable the oscillator; and wherein said arrangement further includes a first amplifying device connected between the oscillator and said first rectifying arrangement and a second amplifying device connected between the oscillator and said second rectifying arrangement.

3. A pulse correcting arrangement according to claim 1, wherein said adjustable means includes an auxiliary winding on said pulse repeating relay, a potentiometer connected across said auxiliary winding, a center tap to said auxiliary winding, a sliding tap on said potentiometer, said taps being connected to the opposite poles respectively of a source of direct-current.

4. A pulse correcting arrangement according to claim 1, wherein each of said thyratrons includes a cathode, a control grid, and a plate, said side contacts being coupled respectively to said grids, said receiving relay being connected between said plates, a capacitor connected be tween said cathodes, and said means for cutting off either thyratron comprising means for sending a positive pulse through said capacitor.

5. A pulse correcting arrangement according to claim 4, wherein said detecting and indicating means comprises a rotating disk, and two lamps mounted on said disk, said two lamps being connected in the cathode circuits respectively of said thyratrons.

6. A pulse correcting arrangement according to claim 1, wherein said detecting and indicating means comprises a disk, a synchronous motor rotating said disk, an oscillater for supplying current to said motor at a frequency such that the disk is rotated in synchronism with the character repetition rate of the received telegraph signals, two lamps mounted on said disk circumferentially displaced by of the circumference and radially by an appreciable distance, said lamps being lighted in accordance with the repeated mark and space pulses, respectively.

7. A pulse correcting arrangement according to claim 6, wherein said two lamps are connected respectively, one in the circuit of one of said thyratrons and the other in the circuit of the other thyratron.

References Cited in the tile of this patent UNITED STATES PATENTS 1,969,573 Montgomery et al Aug; 7, 1934 1,971,148 Wise Aug. 21, 1934 2,173,740 Wilder Sept. 19, 1939 2,468,556 Hurault Apr. 26, 1949 2,599,345 Oberman et a1. June 3, 1952 2,712,038 Carver June 28. 1955 

